surgeongirl wrote:I am not trained in genetics but what intrigued me was this equation by author

But look at the man. He is something more. He is X and Y. That means, he is essentially an ‘X ’plus something extra. What do I mean by that! Man is already a woman that is ‘X’, plus something extra. Does that mean first step towards manhood is womanhood? Now let’s talk in mathematical language. Here is the equation, Man = 22 autosomes + X + Y Woman= 22 autosomes + X + X= 22 autsomes + X (by logic not by mathematics). . . Man= (22 autosomes + X) + Y= Woman + Y (by mathematics, simply) So man is everything that woman is, plus something extra. Now the extra thing is not qualitatively different, but quantitatively. Hence Y here must be somewhat like X + 1, X+2 or X+ 3 or something like that. It would be ultimately proven that woman can potentially grow into man. Similarly man can reduce to woman, if he loses some part of ‘Y’.

This isn't really maths. It's just using equations as bad analogies.

Note that the Y chromosome is structurally pretty much the X chromosome with parts removed. So the conclusion is wrong. Y isn't X with something extra. It's arguably better understood as X with something removed.

It's important to note that genes are not blueprints. Many of the genes for gender related structure and physiology are not on the X or the Y chromosomes at all, but on other chromosomes altogether. Development of a body involves all kinds of cascades of gene activations across many chromosomes; much of what happens with X and Y is simply genetic switches. There are genes on the Y chromosome (SRY in particular) which are not in the X chromosome; and this gene does act as a switch for many other genes use in development of sex organs.

I tend to concur with Darby; this notion doesn't make much sense in the light of exiting knowledge of genetics and sex.

I'd recommend this as relevant and easy to read: DNA basics: ask a geneticist Q456, in which Jessica Profato answers a question (March 2012) from an elementary school student:What is the big difference about the X and Y chromosomes that make the difference between male and female people? Do the cells just generate differently?

Hi Cat... menopause is a great example to consider, but there isn't an easy answer to it.

The problem with your proposal is that evolution doesn't actually work for the good of the species; except as a side effect of benefits for the individual.

Preventing late reproduction by lowering the chance of passing on damaged genetic material is not an adequate answer; because from the perspective of the individual, passing on damaged DNA is still much much better than passing on none at all.

There is a considerable literature of evolution of menopause; but it is largely hypothetical since it is so difficult to come up with ways to test the various hypotheses.

One of the best known serious proposals to explain the evolution of menopause is the grandmother hypothesis. The central idea is that for older women, the individual fitness benefit from having new children is actually less that the fitness benefit obtained by devoting effort to the raising of the grandchildren. If a mother dies -- as is more likely with age, of course! -- any dependent children will probably die as well. So the fitness benefit of children in old age is substantially reduced.

As a hypothesis this sounds plausible; but mere plausibility is not enough for an explanation to be truly scientific. Testing the model in more detail requires careful calculation and measurement bearing on the fitness consequences of menopause. There has been a fair bit of work on this: some supportive, and some conflicting, with the grandmother hypothesis. Wikipedia has a fair summary of the idea: Wikipedia: Grandmother Hypothesis.

Other ideas have been proposed also. A recent publication in PLoS Computational Biology proposes that menopause is a side effect of mating choices by males for younger females. See: Morton RA, Stone JR, Singh RS (2013) Mate Choice and the Origin of Menopause. PLoS Comput Biol 9(6): e1003092. doi:10.1371/journal.pcbi.1003092. The idea is that menopause is the result of an accumulation of detrimental mutations, which become fixed because there is little selection AGAINST them; due to the mating preference against older females. There's a lot more in the paper. The hypothesis is tested using computational models and various assumptions for mate selection and other factors. There's no field testing, however; that would be the obvious next step.

ChrisHoStuart wrote:Hi Cat... menopause is a great example to consider, but there isn't an easy answer to it.

The problem with your proposal is that evolution doesn't actually work for the good of the species; except as a side effect of benefits for the individual.

Preventing late reproduction by lowering the chance of passing on damaged genetic material is not an adequate answer; because from the perspective of the individual, passing on damaged DNA is still much much better than passing on none at all.

There is a considerable literature of evolution of menopause; but it is largely hypothetical since it is so difficult to come up with ways to test the various hypotheses.

One of the best known serious proposals to explain the evolution of menopause is the grandmother hypothesis. The central idea is that for older women, the individual fitness benefit from having new children is actually less that the fitness benefit obtained by devoting effort to the raising of the grandchildren. If a mother dies -- as is more likely with age, of course! -- any dependent children will probably die as well. So the fitness benefit of children in old age is substantially reduced.

As a hypothesis this sounds plausible; but mere plausibility is not enough for an explanation to be truly scientific. Testing the model in more detail requires careful calculation and measurement bearing on the fitness consequences of menopause. There has been a fair bit of work on this: some supportive, and some conflicting, with the grandmother hypothesis. Wikipedia has a fair summary of the idea: Wikipedia: Grandmother Hypothesis.

Other ideas have been proposed also. A recent publication in PLoS Computational Biology proposes that menopause is a side effect of mating choices by males for younger females. See: Morton RA, Stone JR, Singh RS (2013) Mate Choice and the Origin of Menopause. PLoS Comput Biol 9(6): e1003092. doi:10.1371/journal.pcbi.1003092. The idea is that menopause is the result of an accumulation of detrimental mutations, which become fixed because there is little selection AGAINST them; due to the mating preference against older females. There's a lot more in the paper. The hypothesis is tested using computational models and various assumptions for mate selection and other factors. There's no field testing, however; that would be the obvious next step.

Other species have displayed similar processes to menopause as well if they are able to live past the age of reproduction. However, if I remember correctly it's only been observed in primates and we have a different life history than other mammals. In humans primarily, women have a much longer period for reproduction

How does an organism determine when to stop reproducing based on their chances of mating? Females have a set number of follicles they are born with. Though, I do see how that hypothesis makes sense if by chance alone the mutation was increased. (admittedly I didn't read the whole thing as I plan on passing out to sleep soon) However, if something is neither selected for or against, how did the mutations reach fixation? I suppose it could happen just by chance alone...but I'll have to read it to see their support.

We have a limited follicle pool and therefore no longer need to menstruate once we are no longer ovulating. The size of the organism is a limiting factor in females because we don't create new gametes every day like males. There is no advantage in growing extra large ovaries with a large pool of follicles because, like that hypothesis mentions, men select for younger women to reproduce with.

A tomato tree is growing . Its not male or female. Its just a tree. Letz call it male. Now the season change .The flowers are ripening into red tomatoes. The tree itself feel different from within . The structure is same only the feelings are different . Its blushing like a woman. But wait . Its not going to last like this. Soon the tomatoes will fall. Aloha its a male again,(ref. Man is the extension of woman)